1. Technical Field
The present invention relates to an illumination apparatus for illuminating, for example, a light modulation element, a projector for projecting and displaying an optical image, which is provided to, for example, a light modulation element, on a screen with a projection lens, and an illumination method, and more specifically to a configuration of an illumination optical system of an illumination apparatus and a projector provided with a plurality of light source sections.
2. Related Art
A projector illuminating a small-sized light modulation element, which forms an optical image in accordance with image information, with light from an illumination apparatus, and projecting the optical image on a screen or the like with a projection lens has been put into practical use as one of apparatuses capable of displaying a large-screen image. For such a projector, there have been strongly desired growth in size of the screen and improvement in the luminance of the projection image, and reduction of the luminance variation and the color variation, and high-performance illumination optical systems capable of realizing these desires have been under development.
For example, in the projection display apparatus (projector) disclosed in JP-A-6-265887 (Document 1, see in particular FIG. 1), improvement in the intensity of the light for illuminating a light valve (a light modulation element) is achieved using two light source sections. Further, this projection display apparatus is provided with integrator optical systems corresponding respectively to the light source sections, thereby achieving reduction of the luminance variation and the color variation of the illumination light. Optical elements such as light modulation elements and polarization elements represented by liquid crystal light valves, or projection lenses each have an optical characteristic having an angular dependency on incident light. Therefore, in order for achieving improvement in the image quality of the display image, it is desirable to use a light source section capable of emitting illumination light with a narrow spread of the angular distribution.
However, according to the configuration of this projector, since the two light source sections are disposed at locations substantially distant from the illumination optical axis, the angular distribution of the illumination light spreads widely, and two groups of light source images formed on the pupil plane of the projection lens are formed at locations distant from the projection optical axis. As a result, degradation of the contrast of the display image is caused, and it is not successful to improve the luminance of the display image so much as expected. Further, since the imaging performance of the projection lens is high in the vicinity of the projection optical axis and drops in accordance the distance from the projection optical axis, the imaging performance of the projection lens cannot sufficiently be exerted, and deterioration of the image quality of the display image is caused. Further, in the case in which the emission characteristics of the two light source sections are different from each other, the luminance variation and the color variation due to the difference in the form of vignetting of the projection light caused by the vignetting of the projection lens occur in the display image.
JP-A-2000-3612 (Document 2, see in particular FIG. 1) discloses a projection display apparatus (a projector) achieving elimination of the problems described above. The illumination optical system used here has a configuration provided with two light source sections each formed of an ellipsoidal reflector having the first focal point in the vicinity of the light emitter, and reflecting prisms (reflecting surfaces) disposed at the second focal points of the respective ellipsoidal reflectors, and thereby reflecting light beams from the respective light source sections towards the integrator with the reflecting prisms. Thus, the position of the secondary light source image of the light emitter formed on the reflecting surface of the reflecting prism comes closer to the illumination optical axis than the position of the original light emitter. Since in the subsequent part of the optical system the position of the secondary light source image can be assumed as the light source position and thus treated, an arrangement equivalent to the arrangement in which the two light source sections are disposed substantially closely to the illumination optical axis is achieved, and it becomes possible to improve the problems described above.
However, in the illumination apparatus described in the Document 2, the light source images formed on the pupil plane of the projection lens are still formed at positions distant from the projection optical axis. The reason therefor is as follows. That is, forming the secondary light source images of the respective light source sections at positions close to the illumination optical axis as much as possible is exactly the same as forming the respective secondary light source images at positions close to an apex of the reflecting prism. However, since the secondary light source image has a certain finite size, the reflecting surface is required to have an appropriate area, and it is not achievable to reflect the light beam in the nearest neighbor area of the apex of the reflecting prism. Therefore, most part of the light source image is still located in other areas than on the projection optical axis where the projection lens exerts the highest imaging performance, and the improvement effect of the problems can be expected, but is not necessarily sufficient in comparison with the case with the projector disclosed in the Document 1 described above.